Preparation of photopolymeric gravure printing plates

ABSTRACT

Photopolymeric gravure printing plates which are to be developed with water or water/alcohol mixtures after imagewise exposure and have, arranged one on top of the other on a dimensionally stable substrate, a layer (A) which may be bonded to the dimensionally stable substrate by an adhesion-promoting layer and is crosslinkable by actinic radiation, a layer (B) which is sensitive to IR radiation and, if required, a parting layer arranged between layer (A) and layer (B), and a peelable protective film applied to the layer (B), are produced by a process in which the layer (A) consists of a mixture of at least one polymeric binder which is soluble or dispersible in water or water/alcohol mixtures, copolymerizable ethylenically unsaturated organic compounds which are compatible with this polymeric binder, a photoinitiator or photoinitiator system and, if required, further assistants, the parting layer which may be arranged between layer (A) and layer (B) is oxygen-permeable and the layer (B) sensitive to IR radiation has an optical density ≧2.5 in the actinic range and contains a film-forming polymeric binder which is soluble or dispersible in water or water/alcohol mixtures and at least one substance which is finely distributed in this binder, absorbs IR radiation and has a high absorbence in the wavelength range from 750 to 20,000 nm, the layer (B) sensitive to IR radiation is structured by laser ablation after the protective film has been peeled off and is then exposed uniformly to actinic radiation, developed with water or water/alcohol mixtures and dried in a conventional manner. 
     The novel process is suitable for the production of gravure printing plates.

This is a division of application Ser. No. 08/721,536, filed Sep. 26,1996, now U.S. Pat. No. 5,994,032.

The present invention relates to a process for the production ofphotopolymeric gravure printing plates which are to be developed withwater or water/alcohol mixtures after imagewise exposure and have,arranged one on top of the other on a dimensionally stable substrate, alayer (A) which may be bonded to the dimensionally stable substrate byan adhesion-promoting layer and is crosslinkable by actinic radiation, alayer (B) sensitive to IR radiation, if required a parting layerarranged between layer (A) and layer (B), and a peelable protective filmapplied to the layer (B), and are suitable for digital informationtransfer, and gravure printing plates produced by this process.

Photopolymeric gravure printing plates which can be developed with wateror with an aqueous alcoholic medium consist of a photosensitivephotopolymerizable layer which is soluble or dispersible in thedeveloper and is applied to a dimensionally stable substrate, forexample polyethylene terephthalate film or steel or aluminum sheet. Inorder to provide a firm bond, an adhesion-promoting layer may be appliedbetween the photosensitive, photopolymerizable layer which can bedeveloped with water or an aqueous alcoholic medium and the substrate.

A release layer may also be present on the photosensitive,photopolymerizable layer which can be developed with water or an aqueousalcoholic medium, said release layer being required whenever said layerpresent underneath is so tacky that, when the photographic negative isplaced on top, the air present in the vacuum printing frame cannot beuniformly removed and consequently vacuum errors occur during exposure.

The photosensitive, photopolymerizable layer which can be developed withwater or an aqueous alcoholic medium can be protected from mechanicaldamage by a protective film which is present either on said layer or onthe release layer present thereon (cf. for example Ullmannn'sEncyclopedia of Industrial Chemistry, Vol. A 13, page 629).

The information contained in the photographic negative is transferred tothis photosensitive, photopolymerizable layer which can be developedwith water on an aqueous alcoholic medium, in general after removal ofthe protective film, if present, by application of the photographicnegative, removal of the air by means of a vacuum frame and uniformexposure. The well depth of the gravure printing plate and hence theamount of ink transferred during the printing process are controlled bymeans of the exposure time.

In the subsequent development step, the unpolymerized parts, the wells,can be washed out with the aid of water or water/alcohol mixtures; thephotopolymerized parts are insoluble or nondispersible and thus form thesurface of the gravure printing plates. In order to remove the water orthe water/alcohol mixture from the swollen relief layer, a subsequentdrying step is effected. Depending on the photosensitive material, theplate may require further processing steps. In the case of some printingplates, for example, uniform post exposure is required in ordercompletely to cure the printing plates.

In this process, the information is thus transferred via a photographicnegative. According to the prior art, photographic negatives areproduced by exposure of a photosensitive film by means of an exposureunit, for example an optomechanical exposure unit, a CRT (cathode raytube) exposure unit or a laser exposure unit (He—Ne laser, λ=632 nm),with subsequent development (cf. for example Armin Lautert, AllgemeineFachkunde der Drucktechnik, pages 42-45, 11th Edition 1993, Baden-verlagCH-Baden).

The information transferred in this manner to the film originates from adigitized data set. In rotary gravure printing, the printing platecannot be produced in seamless and continuous form by the use of anegative.

For these reasons, it would be desirable to be able to produce a gravureprinting plate without the circuitous route via a photographic negative.

In addition to the shorter production times, the costs for theproduction of a photographic negative would not be incurred. Inaddition, the wet chemical processes in film development would no longerbe required. This would be associated with the ecological advantage thateffluents contaminated with chemicals and metal salts would no longer beproduced.

Furthermore, the geometric dimensions of a photographic negative maychange as a result of the temperature and atmospheric humidity, whichmay lead to register problems of the finished gravure printing platesince, when a corresponding photosensitive, photopolymerizable layer isexposed, the information of the photographic negative is transferred asa 1:1 projection. According to the prior art, UV exposure is carried outthrough a photographic negative with application of a vacuum, sinceintensive contact is required between negative and plate surface inorder to avoid side lighting and copying errors. The pressure requiredfor the intensive contact between plate surface and negative may pressin the dust particles and hence lead to holes in the plate surface whichsubsequently transfer ink in an undesirable manner in the printingprocess.

However, UV exposure without reduced pressure would be desirable, inorder to be able to utilize the inhibitory effect of the atmosphericoxygen, to be able to control the well depths with less scattering andto avoid the surface defects caused by dust particles.

Digital processes in which no photographic negative is required forinformation transfer have long been known.

For example, DE 4117127 A1 describes a process in which an image-bearingmask is produced on photosensitive recording elements by using an inkjetprinter or an electrophotographic printer. The disadvantage here is thatthe resolution is insufficient for high-quality gravure printing.

EP 0001138-A1 describes a process for the production of lithographicprinting plates with formation of a fugitive negative.

WO 94/03839 describes a process in which the photosensitive recordingelement is structured by means of an IR laser and an image-bearing maskis produced in this manner. Here, the photosensitive recording materialconsists of a substrate, a photosensitive layer, an IR-sensitive layerwhich is opaque to actinic light and a release layer. On exposure to theIR laser, the exposed parts of the IR-sensitive layer are fixed to therelease layer on top and can be removed together with the release layerby peeling off the latter. An image-bearing mask on the photosensitiverecording layer is thus obtained. The disadvantage here is that damage,for example scratches in the release layer, which are simultaneously toserve for mechanical protection, leads to defective informationtransfer. Furthermore, particularly in the case of fine image sections,there is the danger that surrounding parts that remain on thephotosensitive recording material may be damaged when the release layeris peeled off, likewise leading to defective information transfer. U.S.Pat. No. 5,262,275 and WO 94/03838 describe a process in whichflexographic printing plates are provided with a digital structure bymeans of an IR laser. The recording element consists of a substrate, aphotosensitive flexographic layer, a barrier layer and an IR-sensitivelayer which is opaque to actinic light. The IR-sensitive layer isrecorded on directly by means of the IR laser, the IR-sensitive materialbeing evaporated in the parts recorded on and these parts thus becomingtransparent to actinic light. The barrier layer present under theIR-sensitive layer on the one hand protects the IR-sensitive layeragainst diffusion of monomers and other components from the UV-sensitiveflexographic layer and prevents the entry of oxygen into theUV-sensitive flexographic layer during UV exposure. As described in WO94/03838, the UV exposure is not reproducible in the presence ofatmospheric oxygen. Moreover, longer exposure times are required in thepresence of oxygen. Hence, barrier layers which are not permeable tooxygen are used.

It is an object of the present invention to provide a gravure printingplate which can be developed with water or an aqueous alcoholic medium,can be provided with digital recordings by means of an IR laser and, ina subsequent step, can be uniformly exposed to UV light with goodreproducibility without reduced pressure.

We have found, surprisingly, that this object is achieved by the novelprocess, a photosensitive recording material which can be developed withwater or an aqueous alcoholic medium overcoming the stateddisadvantages.

The present invention relates to a process for the production ofphotopolymeric gravure printing plates which are to be developed withwater or water/alcohol mixtures after imagewise exposure and have,arranged one on top of the other on a dimensionally stable substrate, alayer (A) which may be bonded to a dimensionally stable substrate by anadhesion-promoting layer and is crosslinkable by actinic radiation, alayer (B) which is sensitive to IR radiation and, if required, a partinglayer arranged between layer (A) and layer (B), and a peelableprotective film applied to the layer (B), wherein the layer (A) consistsof a mixture of at least one polymeric binder which is soluble ordispersible in water or water/alcohol mixtures, copolymerizableethylenically unsaturated organic compounds which are compatible withthis polymeric binder, a photoinitiator or photoinitiator system and, ifrequired, further assistants, the parting layer which may be arrangedbetween layer (A) and layer (B) is oxygen-permeable and the layer (B)sensitive to IR radiation has an optical density ≧2.5 in the actinicrange and contains a film-forming polymeric binder which is soluble ordispersible in water or water/alcohol mixtures and at least onesubstance which is finely distributed in this binder, absorbs IRradiation and has a high absorbence in the wavelength range from 750 to20,000 nm, the layer (B) sensitive to IR radiation is structured bylaser ablation after the protective film has been peeled off and is thenexposed uniformly to actinic radiation, developed with water orwater/alcohol mixtures and dried in a conventional manner.

The uniform exposure to actinic radiation can preferably be carried outwithout the use of reduced pressure.

The present invention furthermore relates to gravure printing plateswhich were produced by the novel process.

The novel recording element is very useful for digital informationtransfer.

Suitable dimensionally stable substrates are those usually used for theproduction of gravure printing plates.

Examples of suitable dimensionally stable substrates are plates, sheetsand conical and cylindrical sleeves of metals, such as steel, aluminum,copper or nickel, or of plastics, such as polyethylene terephthalate,polybutylene terephthalate, polyamide and polycarbonate, woven fabricsand nonwovens, such as glass fiber fabrics, and composite materialscomprising glass fibers and plastics.

Particularly suitable dimensionally stable substrates are dimensionallystable substrate sheets and metal sheets, for example polyethylene orpolyester sheets or steel, stainless steel or aluminum sheets. Thesesubstrate sheets are generally from 50 to 1100 μm, preferably from 75 to700 μm, for example about 300 μm, thick.

These substrate sheets may be coated with a thin adhesion-promotinglayer, for example 1-5 μm thick layer, on that side of the substratesheet which faces the photosensitive recording layer. Thisadhesion-promoting layer may consist, for example, of a mixture of apolycarbonate, of a phenoxy resin and a polyfunctional isocyanate.

The photostructurable layer (A) may be present on the dimensionallystable substrate, if necessary also by means of an adhesion-promotinglayer and an upper coating.

For example, polyurethane adhesive coatings (for example according toDE-A-30 45 516) based on polyisocyanate-crosslinked polyether orpolyester coatings may serve as adhesion-promoting layers, in layerthicknesses of from 0.5 to 50 μm, in particular from 2 to 30 μm.

Upper coatings may be present on that side of the adhesion-promotinglayer which faces away from the substrate, have layer thicknesses offrom 0.1 to 50 μm, in particular from 1 to 10 μm, and may be obtained,for example, from a dilute aqueous/alcoholic solution of partiallyhydrolyzed (eg. to an extent of 80 mol %) polyvinyl ester, phenylglycerol ether monoacrylate and glyoxal, with drying and baking.

The relief-forming layer (A) crosslinkable by actinic radiation, ie.photostructurable, is, according to the invention, a mixture of at leastone polymeric binder which is soluble or dispersible in water orwater/alcohol mixtures, copolymerizable ethylenically unsaturatedorganic compounds compatible with this polymeric binder, aphotoinitiator or photoinitiator system and, if required, furtherassistants and additives, such as thermal polymerization inhibitors,plasticizers and/or colorants, suitable alcohols in the water/alcoholmixtures being methanol, ethanol, n-propanol and isopropanol, preferablyethanol.

Suitable polymeric binders are the ones usually used for the productionof printing plates, such as completely or partially hydrolyzed polyvinylesters, for example partially hydrolyzed polyvinyl acetates, polyvinylalcohol derivatives, eg. partially hydrolyzed vinyl acetate/alkyleneoxide graft copolymers, or polyvinyl alcohols subsequently acrylated bya polymer-analogous reaction, as described, for example, inEP-A-0079514, EP-A-0224164 or EP-A-0059988, and mixtures thereof.

Also suitable as polymeric binders are polyamides which are soluble inwater or water/alcohol mixtures, as described, for example, inEP-A-0085472 or DE-A-1522444.

In the photostructurable layer (A), these polymer binders account for ingeneral from 50 to 98, preferably from 60 to 95, % by weight of thetotal amount of the photostructurable layer (A). Suitablecopolymerizable ethylenically unsaturated organic compounds are thosewhich are compatible with the polymeric binders chosen in each case. Ingeneral, these are mono- and/or polyolefinically unsaturated organiccompounds at room temperature, in particular derivatives of acrylicand/or methacrylic acid, such as esters thereof with mono- or polyhydricalcohols, for example acrylates or methacrylates of alcanols of 1 to 20carbon atoms, such as methyl methacrylate, ethyl acrylate, propyl(meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate,isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl(meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylateor lauryl (meth)acrylate, (meth)acrylates of polyhydric alcohols of 2 to20 carbon atoms, eg. 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycoldi(meth)acrylate, butane-1,4-diol di(meth)acrylate, neopentylglycoldi(meth)acrylate, 3-methylpentanediol di(meth)acrylate,1,1,1-trimethylolpropane tri(meth)acrylate, di-, tri- and tetraethyleneglycol di(meth)acrylate, tripropylene glycol di(meth)acrylate orpentaerythrityl tetra(meth)acrylate, and poly(ethylene oxide)di(meth)acrylate, ω-methylpoly(ethylene oxide)-yl (meth)acrylate,N,N-diethylaminoethyl acrylate, a reaction product of 1 mol of glycerol,1 mol of epichlorohydrin and 3 mol of acrylic acid, and glycidylmethacrylate and bisphenol A diglycidyl ether acrylate.

Derivatives of acrylamide and of methacrylamide are also suitable, forexample ethers of their N-methylol derivatives with mono- and polyhydricalcohols, eg. ethylene glycol, glycerol, 1,1,1-trimethylolpropane oroligomeric or polymeric ethylene oxide derivatives. These areparticularly suitable if polyamides or polyvinyl alcohol are used asbinders.

Also suitable are epoxide (meth)acrylates and urethane (meth)acrylates,as can be obtained, for example, by reacting bisphenol A diglycidylether with (meth)acrylic acid or by reacting diisocyanates withhydroxyalkyl (meth)acrylates or with hydroxyl-containing polyesters orpolyethers. Olefinically unsaturated organic compounds which mayfurthermore be used are esters of acrylic or methacrylic acid, inparticular those having a low vapor pressure and those which aremodified with compatibilizers, for example with hydroxyl, amido,sulfoester or sulfonamido groups. Mixtures of the above-mentionedcopolymerizable ethylenically unsaturated organic compounds may also beused. Said compounds may be present in the photostructurable layer inamounts of from 1 to 60, preferably from 10 to 45, % by weight, based onthe total amount of the photostructurable layer.

Suitable photoinitiators or photoinitiator systems are those generallyused for photosensitive recording materials, for example free radicalphotoinitiators, eg. benzoin or benzoin derivatives, such as benzoinethers or straight-chain or branched monoalcohols of 1 to 6 carbonatoms, eg. benzoin methyl ether, benzoin ethyl ether, benzoin isopropylether, benzoin n-butyl ether or benzoin isobutyl ether, symmetrically orasymmetrically substituted benzil acetals, such as benzil dimethylacetal or benzil 1-methyl 1-ethyl acetal, diarylphosphine oxides, suchas 2,4,6-trimethylbenzoyldiphenylphosphine oxide or2,6-dimethoxybenzoyldiphenylphosphine oxide, ethyl2,4,6-trimethylbenzoylphenylphosphinate or acyldiarylphosphine oxidesaccording to German Laid-Open Application DOS 2,909,992, diacylphosphineoxides or substituted and unsubstituted quinones, such asethylanthraquinone, benzanthraquinone, benzophenone or4,4′-bis(dimethylamino)benzophenone. They may be used alone or as amixture with one another or in combination with coinitiators, forexample ethylanthraquinone with 4,4′-bis(dimethylamino)benzophenone,benzoin methyl ether with triphenylphosphine, diacylphosphine oxideswith tertiary amines or acyldiarylphosphine oxides with benzil dimethylacetal.

The photoinitiators are present in the photostructurable layer (A)usually in amounts of from 0.1 to 10, preferably from 0.5 to 5, % byweight, based on the total amount of the photostructurable layer.

In addition to polymeric binders, copolymerizable olefinicallyunsaturated organic compounds and photoinitiators, the photostructurablelayer (A) may contain further assistants and additives, for example from0.001 to 2% by weight, based on the total amount of thephotostructurable layer, of thermal polymerization inhibitors which haveno significant self-absorption in the actinic range in which thephotoinitiator absorbs may be added, eg. 2,6-di-tert-butyl-p-cresol,hydroquinone, p-methoxyphenol, β-naphthol, phenothiazine, pyridine,nitrobenzene, m-dinitrobenzene or chloranil; thiazine dyes, such asThionine Blue G (C.I. 52025), Methylene Blue B (C.I. 52015) or ToluidineBlue (C.I. 52040); or N-nitrosamines, such as N-nitrosodiphenylamine, orthe salts, for example the potassium, calcium or aluminum salts, ofN-nitrosocyclohexylhydroxylamine.

Suitable dyes, pigments or photochromic additives may also be added tothe novel photostructurable layer (A) in an amount of from 0.0001 to 2%by weight, based on the mixture of the layer (A). They are used forcontrolling the exposure properties, for identification, for directmonitoring of the exposure result or for aesthetic purposes. Aprecondition for the choice and the amount of such additives is thatthey have just as little an adverse effect on the photopolymerization ofthe mixtures as do the thermal polymerization inhibitors. For example,the soluble phenazinium, phenoxazinium, acridinium and phenothiaziniumdyes, such as Neutral Red (C.I. 50040), Safranine T (C.I. 50240),Rhodanil Blue, the salt or amide of Rhodamine D (Basic Violet 10, C.I.45170), Methylene Blue B (C.I. 52015), Thionine Blue G.(C.I. 52025), orAcridine Orange (C.I. 46005), and Solvent Black 3 (C.I. 26150) aresuitable. These dyes may also be used together with a sufficient amountof a reducing agent which does not reduce the dye in the absence ofactinic light but is capable of reducing the dye in the excitedelectronic state on exposure. Examples of such mild reducing agents areascorbic acid, anethole, thiourea, eg. diethylallylthiourea, inparticular N-allylthiourea, and hydroxylamine derivatives, in particularsalts of N-nitrosocyclohexylhydroxylamine, preferably the potassium,calcium and aluminum salts. As stated, the latter may simultaneouslyserve as thermal polymerization inhibitors. The reducing agents may beadded in general in amounts of from 0.005 to 5% by weight, based on themixture of the layer (A), the addition of from 3 to 10 times the amountof concomitantly used dye having proven useful in many cases.

To increase the scratch resistance and abrasion resistance, finelydivided, hard, abrasive particles, as described in DE-A-3128949 (EP070511), may be added. For example silicas, in particular quartz powder,silicates, such as aluminum silicates or silicate glasses, aluminas, inparticular corundum, titanium dioxide and/or carbides, such as siliconcarbide or tungsten carbide, may be used as abrasive particles.

The production of the photostructurable layer (A) from the individualcomponents can be carried in the conventional manner by mixing thecomponents with the aid of known mixing methods and by processing thismixture to give the photostructurable layer by means of knowntechniques, such as casting from solution, calendering or extrusion, andthese measures may also be combined with one another in a suitablemanner. The thickness of the photostructurable layer is advantageouslyfrom about 0.03 to 2 mm, in particular from 100 μm to 1000 μm.

The layer (B) which is sensitive to IR radiation and laser-ablatableand, if required, an intermediate layer comprising an oxygen-permeabledeveloper-soluble or developer-dispersible polymer are present on thephotostructurable layer.

Such an intermediate layer is capable of reducing the diffusion ofmonomers from the photosensitive, photopolymerizable layer into theIR-sensitive layer (B) thereon and of protecting the photosensitive,photopolymerizable layer from the action of the laser beam during thelaser ablation. Moreover, this intermediate layer is permeable toatmospheric oxygen so that atmospheric oxygen can gain access during theUV-exposure following the laser ablation and more exact control of thewell depth is thus achieved.

Examples of such water- or water/alcohol-soluble or dispersible polymerssuitable as oxygen-permeable intermediate layers are partiallyhydrolyzed polyvinyl esters, for example partially hydroxylzed polyvinylacetates, polyvinyl alcohol derivatives, such as partially hydrolyzedvinyl acetate/alkylene oxide graft copolymers, maleic anhydridecopolymers, such as copolymers of maleic anhydride and isobutene ormaleic anhydride and vinyl methyl ether, water-soluble polyesters,water-soluble polyethers, homo- and copolymers of vinylpyrrolidone,vinylcaprolactam, vinylimidazole, vinyl acetate and acrylamide,water-soluble polyurethanes, polyamides which are soluble in water orwater/alcohol mixtures, and mixtures of these polymers.

The layer (B) sensitive to IR radiation consists of one or morewater-soluble or water-dispersible or water/alcohol-soluble or-dispersible binders, an IR-absorbing material which is finelydistributed in this binder and has strong absorption in the wavelengthrange from 750 to 20,000 nm, preferably from 750 to 5000 nm, and, ifrequired, a plasticizer. The IR-sensitive layer (B) has an opticaldensity of ≧2.5, preferably from 3 to 5, in relation to actinic light.

Examples of such binders are partially hydrolyzed polyvinyl esters, forexample partially hydrolyzed polyvinyl acetates, polyvinyl alcoholderivatives, such as partially hydrolyzed vinyl acetate/alkylene oxidegraft copolymers, maleic anhydride copolymers, eg. copolymers of maleicanhydride and isobutene or maleic anhydride and vinyl methyl ether,water-soluble polyesters, water-soluble polyethers, homo- and copolymersof vinylpyrrolidone, vinylcaprolactam, vinylimidazole, vinyl acetate andacrylamide, water-soluble polyurethanes, polyamides which are soluble inwater or in water/alcohol mixtures, and mixtures of these polymers.

Dyes and/or pigments may be used as IR-absorbing material. The dyes usedmay be, for example, phthalocyanines and substituted phthalocyaninederivatives, cyanine and merocyanine dyes and polymethine dyes. Forexample, carbon black, graphite, chromium oxide and iron oxides may beused as pigments.

The IR-absorbing material is used in a concentration in which it iseffective for the novel application. In general, from 1 to 60% byweight, based on the total weight of the layer (B) sensitive to IRradiation are required.

All compounds which absorb UV light may be used for rendering theIR-sensitive layer (B) impermeable to actinic light. Examples are theabovementioned dyes and pigments. Most initiators in photosensitivelayers are sensitive to UV light. Carbon black is therefore frequentlyused as a pigment in the IR-sensitive layer. When carbon black is usedas a pigment in the IR-sensitive layer, it is possible to dispense withthe use of a further IR-absorbing material. The concentration of thematerial which is impermeable to actinic light is chosen so that therequired optical density is reached. In general, an optical densitygreater than 2.5 is required. When carbon black is used as the pigmentin the IR-sensitive layer (B), from about 1 to 60, preferably from 10 to40, % by weight, based on the total weight of the IR-sensitive layer(B), are used.

Water and/or water-miscible organic solvents, for example alcohols, suchas methanol, ethanol, isopropanol, n-propanol or tetrahydrofuran, arepreferred as solvents for the production of the IR-sensitive layer (B).After combining the components binder, IR-absorbing material and, ifrequired, further assistants, such as plasticizers, surfactants andleveling agents, these are mixed homogeneously with one another in aconventional mixing or dispersing apparatus, such as a stirrer ordissolver. The concentration of the binder and of the IR-absorbingmaterial is from 1 to 80% by weight, based on the total solution. Afterthe solution has been cast on a sheet, for example of polyethyleneterephthalate, the resulting thin film is then dried. The dried film hasa thickness of from 0.5 to 15 μm, preferably from 3 to 10 μm.

The application of the intermediate layer may be effected in a furthercasting step by casting a dilute solution of the binder of theintermediate layer on the IR-sensitive layer and immediately carryingout drying. The thickness of the oxygen-permeable layer may be from 1 to10 μm. The photostructurable layer (A) can then be applied in a furtherstep.

Another process for the production of the novel layer structure startsfrom a gravure printing plate which is produced by the proceduredescribed, in which, if necessary, the intermediate layer is appliedbetween the UV-sensitive layer and the protective film. After removal ofthe protective film, the IR-sensitive layer described above is laminatedwith the intermediate layer, if necessary with the use of a solvent,such as water or a water/alcohol mixture, and, if necessary, said layersare firmly bonded to one another with the aid of a calender.

It is also possible to apply the intermediate layer to the IR-sensitivelayer and to apply the laminate to the gravure printing plate.

The UV light sources (main emission range from 320 to 400 nm) which areusually used for photopolymer printing plates may be employed forexposing the layer (A) crosslinkable by actinic light, for exampleflat-plate exposure units equipped with fluorescent tubes (eg. PhilipsTL 10R 40W or BASF nyloprint 40W BL 366). The 80×107 nyloprint exposureunit is equipped, for example, with 18 high-power UV fluorescent tubesof this type.

Washing out unexposed parts of the photopolymer printing plates,subsequent washing and preliminary drying can be carried out with thecommercial washout systems suitable for this purpose. For example, thenyloprint washout system DW85 operates according to the washoutprinciple employing a brush washer. Drying can then be effected incontinuous dryers, for example in a nyloprint DT85 continuous dryer.

The combination of washout system with continuous dryer is denoted bythe nyloprint DW/DT85 continuous unit.

In the Examples and Comparative Examples which follow, parts andpercentages are by weight, unless stated otherwise.

The production of a novel, photosensitive recording element is describedin Examples 1 and 2.

EXAMPLE 1

A water-soluble IR-sensitive layer (B) was produced by dissolving 2parts of carbon black (eg. Printex® U from Degussa) and 6 parts of apolyvinyl alcohol (eg. Mowiol® 5-72 from Hoechst) in 80 parts of waterand 20 parts of n-propanol. n-Propanol is used as leveling agent inorder to achieve good wetting during casting of this solution on apolyethylene terephthalate sheet. After combination of the components,these were treated in a disperser (Ultra Turrax) for 2 hours in order toprepare a finely divided dispersion. The dispersion thus obtained wascast on a polyethylene terephthalate sheet (125 μm Mylar® from DuPont),this being done in such a way that the resulting film had a layerthickness of 8 μm and an optical density of 4.5 after drying.

This layer was laminated with a commercial water-developable gravureprinting plate on steel sheet, eg. nylograv® WSA 52 (manufacturer BASFAktiengesellschaft) with the use of propanol/water (18:1) as alaminating solvent, after the protective film had been removed from thisplate.

After the protective film had been peeled off, the photosensitiverecording material was mounted on a vacuum drum and exposed by means ofan Nd-YAG laser (wavelength 1064 nm). The spot diameter of the IR beamwas adjusted to 20 μm. This was an exposure unit from Baasel-Scheel.Thereafter, the plate was exposed uniformly to UV light of wavelength320-400 nm without reduced pressure in an 80×107 nyloprint® exposureunit equipped with Philips TL 10R 40W tubes and was washed out withwater in a nyloprint DW/DT 85 continuous unit, dried for 30 minutes at100° C. and postexposed. A printing plate having an excellent gradationof well depths and a scatter of well depths with a constant exposuretime of ±1 μm and giving excellent printed copies was obtained. Thenonprinting parts were absolutely defect-free.

EXAMPLE 2

A water-soluble IR-sensitive layer was produced by dissolving 2 parts ofcarbon black (Printex U from Degussa) and 8 parts of a polyvinyl alcohol(eg. KP 205 from Kuraray) in 80 parts of water and 20 parts ofn-propanol. After combination of the components, these were treated in adisperser (Ultra Turrax) for 2 hours in order to prepare a finelydivided dispersion. The dispersion thus obtained was cast on apolyethylene terephthalate sheet (125 μm thick; eg. Lumirror® from TorayInd.), this being done in such a way that the resulting film had a layerthickness of 8 μm and an optical density of 4.5 after drying.Thereafter, an oxygen-permeable layer was applied to the IR-sensitivelayer, said oxygen-permeable layer being prepared from 45 parts of waterand 2 parts of a partially hydrolyzed polyvinyl alcohol (Mowiol 5-88from Hoechst), cast on the IR-sensitive layer and immediately dried,this being done in such a way that the dried oxygen-permeable layer hada thickness of 6 μm.

This laminate was laminated with a commercial water/alcohol-developablegravure printing plate on steel sheet, eg. nylograv® ST 52 gravureprinting plate (manufacturer BASF Aktiengesellschaft), with the use ofpropanol/water (5:1) as a laminating solvent, after the protective filmhad been removed from this plate.

After the protective film had been peeled off, the photosensitiverecording material was mounted on a vacuum drum and exposed by means ofan Nd-YAG laser (wavelength 1064 nm). The spot diameter of the IR beamwas adjusted to 20 μm. This was an exposure unit from Baasel-Scheel.Thereafter, the plate was exposed uniformly to UV light without reducedpressure in an 80×107 nyloprint® exposure unit and was washed out with a5:1 ethanol/water mixture in a continuous washer operating according tothe principle employing a brush washer, eg. nylograv® DW100 EX/100 (BASFAktiengesellschaft), dried in a dryer, eg. nylograv dryer FII, for 30minutes at 120° C. and then postexposed. A printing plate having anexcellent gradation of well depths and a scatter of well depths with aconstant exposure time of ±1 μm and giving excellent printed copies wasobtained. The nonprinting parts were absolutely defect-free.

COMPARATIVE EXAMPLE 1

A water-developable gravure printing plate (eg. nylograv® WSA 52 fromBASF AG) was, in contrast to Example 1, uniformly exposed in a vacuumframe to UV light through a negative and not through the mask producedby laser ablation of the IR-sensitive layer. Both the negative and themask were produced from the same digital data set; the geometricaldimensions of the image sections permeable to actinic light were thusabsolutely identical in both processes. After the subsequent developmentsteps (washout, drying, postexposure), a printing plate having a coarsegradation of the well depth and a scatter of the well depth withconstant exposure time of ±5 μm was obtained. The finished printingplate was mounted on a printing press and proofs were printed. Theprinted copies corresponded to the prior art, and dust particles whichwere enclosed under the negative and pressed into the surface as aresult of the reduced pressure produced defects during printing.

COMPARATIVE EXAMPLE 2

The IR-sensitive layer was produced as described in Example 1.Thereafter, an oxygen-impermeable layer was applied to the IR-sensitivelayer, said oxygen-impermeable layer being produced from 45 parts ofwater and from 2 parts of a completely hydrolyzed polyvinyl alcohol(Mowiol 66-100 from Hoechst AG), cast on the IR-sensitive layer andimmediately dried, this being done in such a way that the driedoxygen-impermeable layer had a thickness of 6 μm.

This laminate was laminated as in Example 1 with the commercial gravureprinting plate, eg. nylograv® WSA 52, after the protective film had beenremoved from this plate.

This photosensitive recording material produced in this manner wasmounted on a vacuum drum after the protective film had been peeled offand was exposed by means of an Nd-YAG laser (wavelength 1064 nm). Thespot diameter of the IR beam was adjusted to 20 μm. Here too, anexposure unit from Baasel-Scheel was used. Thereafter, the plate wasexposed uniformly to UV light in an 80×107 nyloprint exposure unitwithout a vacuum and was washed out with water in a nyloprint DW/DT 85continuous unit, dried for 30 minutes at 100° C. and postexposed. Aprinting plate having a poor gradation of the well depths and a scatterof the well depths with constant exposure time of ±10 μm was obtained.The printed copy did not meet the requirements for a gravure printingplate.

We claim:
 1. A precursor for a photopolymeric gravure printing platecomprising, arranged one on top of the other i) the substrate layer (S),ii) a layer (A) which is crosslinkable by actinic radiation andcomprises a mixture of a₁) at least one polymeric binder which issoluble or dispersible in water or in a water/alcohol mixture, a₂)copolymerizable ethylenically unsaturated organic compounds which arecompatible with said polymeric binder, a₃) a photoinitiator or aphotoinitiator system, and a₄) optionally further assistants, iii) aparting layer (P), iv) a layer (B) which is sensitive to IR radiation,said layer (B) having an optical density ≧2.5 in the actinic range andcomprising b₁) a film forming polymeric binder which is soluble ordispersible in water or in a water/alcohol mixture and b₂) at least onesubstance which is finely distributed in said film forming binder,absorbs IR radiation and has a high absorbance in the wavelength rangeof from 750 to 20,000 nm, and v) a protective film, said layer (A) beingbonded to the substrate layer (S) either directly or through anadhesion-promoting layer (AS), wherein the film forming polymeric binderb₁) is selected from the group consisting of partially hydrolyzedpolyvinyl esters, partially hydrolyzed vinylacetate/alkylene oxide graftcopolymers, maleic anhydride copolymers, water soluble polyesters, watersoluble polyethers, homo- and copolymers of vinylpyrrolidone,vinylcaprolactam, vinylimidazole, vinyl acetate and acrylamide,water-soluble urethanes, polyamides, and mixtures comprising two or moreof the foregoing.
 2. The precursor defined in claim 1, wherein the IRabsorbing substance b₂) is a dye or a pigment or a mixture thereof. 3.The precursor defined in claim 1, wherein the IR absorbing substance b₂)is selected from the group of phthalocyanines, substitutedphthalocyanine dyes, cyanine dyes, merocyanine dies, polymethine dyes,carbon black, graphite, chromium oxide and iron oxide.
 4. The precursordefined in claim 1, wherein the IR absorbing material is present in anamount of from 1 to 60% by weight, based on the weight of (B).
 5. Theprecursor defined in claim 1, wherein the polymeric binder a₁) isselected from the group consisting of completely or partially hydrolyzedpolyvinylethers, partially hydrolyzed vinyl acetate/alkylene oxide graftcopolymers, acrylated polyvinyl alcohols, polyamides, and mixturescomprising two or more of the foregoing.
 6. The precursor defined inclaim 1, wherein the copolymerizable component a₂) is selected from thegroup consisting of esters of acrylic and methacrylic acid with mono- orpolyhydric alcohols, ethers of N-methylol acrylamide and of N-methylolmethacrylamide with mono- and polyhydric alcohols, epoxide(meth)acrlates and urethane (meth)acrylates, and mixtures comprising twoor more of the foregoing.
 7. The precursor defined in claim 1, whereinthe layer (A) comprises a₁) from 50 to 98% by weight, based on theweight of (A), of the polymeric binder, a₂) from 1 to 60% by weight,based on the weight of (A), of the copolymerizable organic compounds,a₃) from 0.1 to 10% by weight, based on the weight of (A), of thephotoinitiator or photoinitiator system, and a₄) from 0.001 to 2% byweight, based on the weight of (A), of further assistants.
 8. Theprecursor defined in claim 7, further comprising of from 0.0001 to 2% byweight, based on the weight of (A), of dyes, pigments or photochromicadditives.
 9. The precursor defined in claim 7, further comprising offrom 0.005 to 5% by weight, based on the weight of (A), of a reducingagent.
 10. The precursor defined in claim 1, wherein the layer (A) has athickness of from 100 to 1000 μm.
 11. The precursor defined in claim 1,wherein the the parting layer (P) comprises at least one polymerselected from the group consisting of partially hydrolyzed polyvinylethers, maleic anhydride copolymers, water-soluble polyesters,water-soluble polyethers, homo- and copolymers of vinylpyrrolidone,vinylcaprolactam, vinylimidazole, vinylacetate and acrylamide andwater-soluble polyurethanes.
 12. A process for the manufacture of agravure printing plate comprising providing a precursor as defined inclaim 1, removing the protective film, structuring the surface of thelayer (B) from which the protective film has been removed by laserablation, exposing the ablated surface uniformly to actinic radiation,removing the parting layer including residual parts of the layer (B) andnon-exposed parts of the layer (A) by development treatment with wateror a water alcohol mixture, and drying the developed product.
 13. Aprecursor for a photopolymeric gravure printing plate comprising,arranged one on top of the other i) the substrate layer (S), ii) a layer(A) which is crosslinkable by actinic radiation and comprises a mixtureof a₁) at least one polymeric binder which is soluble or dispersible inwater or in a water/alcohol mixture, a₂) copolymerizable ethylenicallyunsaturated organic compounds which are compatible with said polymericbinder, a₃) a photoinitiator or a photoinitiator system, and a₄)optionally further assistants, iii) a parting layer (P), iv) a layer (B)which is sensitive to IR radiation, said layer (B) having an opticaldensity ≧2.5 in the actinic range and comprising b₁) a film formingpolymeric binder which is soluble or dispersible in water or in awater/alcohol mixture and b₂) at least one substance which is finelydistributed in said film forming binder, absorbs IR radiation and has ahigh absorbance in the wavelength range of from 750 to 20,000 nm, and v)a protective film, said layer (A) being bonded to the substrate layer(S) either directly or through an adhesion-promoting layer (AS), whereinthe parting layer (P) comprises at least one polymer selected from thegroup consisting of partially hydrolyzed polyvinyl ethers, maleicanhydride copolymers, water-soluble polyesters, water-solublepolyethers, homo- and copolymers of vinylpyrrolidone, vinylcaprolactam,vinylimidazole, vinylacetate and acrylamide and water-solublepolyurethanes.
 14. The precursor defined in claim 13, wherein thepolymeric binder a₁) is selected from the group consisting of completelyor partially hydrolyzed polyvinylethers, partially hydrolyzed vinylacetate/alkylene oxide graft copolymers, acrylated polyvinyl alcohols,polyamides, and mixtures comprising two or more of the foregoing. 15.The precursor defined in claim 13, wherein the copolymerizable componenta₂) is selected from the group consisting of esters of acrylic andmethacrylic acid with mono- or polyhydric alcohols, ethers of N-methylolacrylamide and of N-methylol methacrylamide with mono- and polyhydricalcohols, epoxide (meth)acrlates and urethane (meth)acrylates, andmixtures comprising two or more of the foregoing.
 16. The precursordefined in claim 13, wherein the layer (A) comprises a₁) from 50 to 98%by weight, based on the weight of (A), of the polymeric binder, a₂) from1 to 60% by weight, based on the weight of (A), of the copolymerizableorganic compounds, a₃) from 0.1 to 10% by weight, based on the weight of(A), of the photoinitiator or photoinitiator system, and a₄) from 0.001to 2% by weight, based on the weight of (A), of further assistants. 17.The precursor defined in claim 16, further comprising of from 0.0001 to2% by weight, based on the weight of (A), of dyes, pigments orphotochromic additives.
 18. The precursor defined in claim 16, furthercomprising of from 0.005 to 5% by weight, based on the weight of (A), ofa reducing agent.
 19. The precursor defined in claim 13, wherein thelayer (A) has a thickness of from 100 to 1000 Am.
 20. A process for themanufacture of a gravure printing plate comprising providing a precursoras defined in claim 13, removing the protective film, structuring thesurface of the layer (B) from which the protective film has been removedby laser ablation, exposing the ablated surface uniformly to actinicradiation, removing the parting layer including residual parts of thelayer (B) and non-exposed parts of the layer (A) by developmenttreatment with water or a water alcohol mixture, and drying thedeveloped product.